As a conventional sound source survey method, sound source survey apparatuses have been developed and commercialized by various audio equipment manufacturers. The sound source survey apparatus is used for visualizing a sound pressure in such a manner that by using a microphone array composed of plural microphones arranged in various shapes, sound pressure distribution is computed at a certain distance on the basis of a sound pressure and phase detected by the microphone array in the principle of beam forming so as to be mapped to an image.
Further, a conventional contribution diagnostic method for examining the level of effects of a sound source or an oscillation source is disclosed in, for example, Japanese Patent Application Laid-Open No. H5-26722. In this method, respective signals of noise or oscillation detected at plural points around an apparatus or the like are input to an adaptive filter, the coefficient of the adaptive filter is updated so as to minimize a difference between the sum of output signals of the adaptive filter and a signal detected at an assessment point where the noise or oscillation is assessed, and the level of the respective sound sources or oscillation sources contributing to the noise or oscillation at the assessment point is displayed using the output signal of the adaptive filter when the difference is converged into a constant value.
However, in the above-described sound source survey method, fluid sound (e.g., blade sound generated when a propeller rotates) due to fluctuations in fluid pressure and oscillation sound (e.g., electromagnetic sound generated by oscillation of a motor) due to oscillation of a structure are mixed and displayed on identified sound pressure distribution, and thus it is impossible to separate the both sound to be displayed.
Further, in the contribution diagnostic method of a sound source or an oscillation source described in Japanese Patent Application Laid-Open No. H5-26722, the level of noise or oscillation contributing to the assessment point of the sound source is merely assessed, and thus it has been desired to effectively and rapidly implement oscillation and noise control and a method for enabling reduction in development period of a noise-free product has been desired.